What you need to know about the ring die of the pellet machine

The ring die is the key part of the pellet machine and the most important wearing part of the pellet machine. According to statistics, the loss of the ring die accounts for more than 25% of the maintenance cost of the entire production workshop, and at the same time has a direct impact on the quality of the extruded pellet feed. Therefore, it is crucial for feed producers to understand the characteristics of the ring die and to make correct selection, reasonable use and effective maintenance of the ring die. The following is a brief analysis of the characteristics of the ring die and its selection, use and maintenance for your reference.

1 Characteristics of ring mold

1.1 Ring mold materials and heat treatment ring mold materials mainly include carbon structural steel, alloy structural steel and stainless steel. Carbon structural steel such as 45 steel, its heat treatment hardness is generally HRC45~ 50, it belongs to the relatively low-grade ring die material, its wear resistance and corrosion resistance are poor; alloy structural steel, such as 20CrMnTi, 40Cr, 35CrMo, etc., the heat treatment hardness is above HRC50, and has good comprehensive mechanical properties. The ring die made of this type of material has high strength and wear resistance, but the disadvantage is that the corrosion resistance is not good; stainless steel materials are X46Cr13 (German brand), 4Cr13, 3Cr13, etc., these materials have good stiffness and toughness, and the heat treatment hardness is greater than HRC50, and has good wear resistance and corrosion resistance, long service life In order to control the hardness uniformity of the ring die after heat treatment, after each ring die heat treatment, take the average hardness of not less than 3 points at each part of the triple in the circumferential direction, and the difference of the hardness value of each part should not be greater than HRC4. In addition, the hardness of the ring mold blank should be controlled, and its hardness should be between HB170 and 220. If the hardness is too high, the drill bit is easy to break when drilling, and cause dead holes, and the hardness is too low. @Miyako smeizhen data @Miyako smeizhen data affects the finish of the mold hole. In order to control the uniformity of the internal material of the blank, if conditions permit, internal flaw detection should be carried out for each blank to prevent cracks, pores, sand inclusion and other defects inside the blank.

1.2 Ring die hole structure, compression ratio and roughness Common ring die holes mainly include straight holes, stepped holes, outer conical holes and inner conical holes. Stepped holes are further divided into release-type stepped holes (commonly known as decompression holes or release holes) and compression-type stepped holes. As shown in Figure 1, different die hole forms are suitable for different types of feed raw materials or different feed formulations. Ring die compression ratio refers to the ratio of the effective length of the ring die hole to the minimum diameter of the ring die hole. It is an indicator reflecting the extrusion strength of pellet feed. The larger the compression ratio, the stronger the extruded pellet feed. For the ring die compression ratio of the straight hole, the effective length of the ring die hole is the total thickness of the ring die, and the minimum diameter is the diameter of the die hole itself; for the release stepped hole and the outer tapered hole, The effective length of the die hole is the total thickness of the ring die minus the length of the release hole or the length of the outer tapered hole, and the aperture of the small diameter segment is the aperture for calculating the compression ratio; for the compressed stepped hole and the inner tapered hole, this situation is relatively special. Generally, the entire ring die thickness is used as the effective length of the die hole, and the minimum diameter is taken as the aperture of the small diameter segment. Of course, this is calculated The meaning of the ring die compression ratio is different from the first two cases. Roughness is also an important indicator to measure the quality of the ring die. Under the same compression ratio, the larger the roughness value, the greater the feed extrusion resistance and the more difficult it is to discharge the feed. Excessive roughness also affects the quality of the particle surface. The appropriate roughness value should be between 0.8 and 1.6.

1.3 The working area of the ring mold, the arrangement of holes and the opening rate @Miyako s1.210.8~ 1.6. 1.3 The working area of the ring mold The product of the inner diameter perimeter of the ring mold and the effective width, the effective width The distance between the two overpass grooves of the ring mold. Under the same working area, the inner diameter of the ring mold is inversely proportional to the effective width. The arrangement of the ring mold when drilling holes is generally arranged in the circumferential direction, and the small holes between the rows and the rows are staggered in the width direction, so that the entire drilled small holes are arranged in an approximate equilateral triangle. If the diameter of the small hole is d, the wall thickness between the small hole and the small hole is a, and the opening rate of the ring mold is φ, then according to the principle of equilateral triangle, it is not difficult to calculate: φ 😉 0.9d2/(d + a) 2 For example, for a ring mold with a small hole diameter of 4.5mm, if the wall thickness between the small holes is 2.6mm, it can be calculated that the opening rate of the ring mold is 36%. As can be seen from the above formula, in order to improve the opening rate of the ring mold under a certain diameter of the mold hole, the wall thickness between the mold holes must be reduced, but the minimum wall thickness must meet the needs of the strength of the ring mold. The general rule is that the larger the die hole diameter, the higher the ring die opening rate.

1.4 Ring die linear velocity Ring die linear velocity refers to the tangential velocity of the inner circle of the ring die. Its height affects the thickness of the material layer in the extrusion zone and the time for the material to pass through the die hole, which in turn affects the output and particle quality of the granulator. When the linear velocity is too high, it may cause the material in the extrusion zone to form faults, the granulation is discontinuous, the resulting particles are soft, and there is a lot of powder, and it is easy to slip for materials with high moisture content, and even cannot be granulated at all; although the lower ring die linear velocity produces good particle quality, it has a great impact on the yield. The commonly used linear speed of the ring die is generally between 6 and 9m/s.

1.5 Ring mold installation method

The installation methods of the ring mold mainly include straight-face installation, tapered installation and hoop installation. The straight-face installation is simple, and the ring mold is not easy to tilt, but the ring mold fixing bolts are easy to cut, so they are not suitable for large-scale granulators. The tapered installation ring mold has good centering performance, large transmission torque, and the ring mold fixing bolts are not easy to cut, but the assembler needs to be careful and master certain skills, otherwise the ring mold is easy to install oblique. The hoop installation is more suitable for small-sized granulators. It is easy to install and takes a short time. The disadvantage is that the ring mold itself is asymmetrical and cannot be used without falling off the surface.

2 Selection of ring die

It can be seen from the characteristics of the ring die that there are many factors to consider when choosing a ring die. But in actual work, usually some factors have already been designed, such as the installation method of the ring die, the linear speed of the ring die and the working area of the ring die, etc., which have been decided when purchasing the pellet machine and generally will not change. Other factors can be guaranteed by choosing a professional ring mold manufacturer, such as the material of the ring mold, the heat treatment strength and wear resistance, the opening rate and roughness of the mold hole. Professional ring mold manufacturers can usually achieve the best performance requirements. Users only need to buy ring molds produced by manufacturers without technical and equipment guarantees for cheap. For example, the processing and heat treatment quality of mold holes can only be guaranteed by special gun drills and vacuum heat treatment equipment. Ordinary drilling machines and heat treatment methods are difficult to process high-quality ring molds.

At present, what is generally faced in feed factories is how to select the appropriate mold hole form and ring mold compression ratio according to the feed varieties and formulas they produce. Generally speaking, straight holes and release stepped holes are suitable for processing compound feed; outer conical holes are suitable for processing high-fiber feeds such as skim bran; inner conical holes and compressed stepped holes are suitable for processing feeds with light specific gravity of grass meal. The reason for the design of the release-type stepped hole mentioned above is that for some varieties of feed, especially small-diameter feed, under the condition of ensuring a reasonable compression ratio, the wall thickness of the ring mold cannot reach the minimum requirement, so that the ring The mold strength is not enough, and the ring mold bursts often in production, and thickening measures have to be taken. The method is to increase the thickness of the ring mold and increase the decompression hole (release hole) at the same time on the premise of ensuring the effective length of the mold hole. For the selection of ring mold compression ratio, due to the different recipes of each company, the raw materials used are different, and the granulation process is also different. The specific and appropriate compression ratio depends on the exploration of each feed manufacturer in production. A rough range is given based on past experience. Generally speaking, the compression ratio between 9 and 13 should be used for livestock and poultry feed; the compression ratio between 13 and 16 should be used for fish feed; the compression ratio between 20 and 25 should be used for shrimp feed; The compression ratio between 7 and 9 should be used for heat-sensitive feeds; the compression ratio between 6 and 9 should be used for forage and straw feeds. In addition, feed producers can also slightly increase or reduce the actual compression ratio according to their own quality requirements. For example, choosing a slightly lower compression ratio is beneficial to increase yield, reduce energy consumption, and reduce the wear of the ring mold, but at the same time reduces the feed quality., if the particles are not strong enough, the pulverization rate is high; on the contrary, it is beneficial to the quality of the particles, such as smooth particle appearance, increased density, and small pulverization rate, but will increase production costs.

3 Use of ring die

Correctly adjusting the working gap between the ring die and the pressing roller is the key to the use of the ring die. Generally speaking, the gap between the ring die and the pressing roller should be between 0.1 and 0.3mm. Under normal circumstances, a slightly larger gap should be used for the matching of the new pressing roller and the new ring die, a smaller gap should be used for the matching of the old pressing roller and the old ring die, a slightly larger gap should be used for the ring die with large aperture, a slightly smaller gap should be used for the ring die with small aperture, a large gap should be used for the material that is easy to granulate, and a small gap should be used for the material that is difficult to granulate. For the operator, it is necessary to have practical operation experience, and the clearance of the ring die can be skillfully selected and adjusted.

In addition, the following points should be paid attention to during the use of the ring die:

① Newly purchased ring molds generally need to be "washed" with oil before starting to remove burrs in the mold holes. If it is a ring mold with a large mold hole of φ 2.5 or more purchased from a regular manufacturer, it may not be carried out. For ring molds with mold holes below φ 2.5, it is generally necessary to "wash the mold" with oil for a few minutes to twenty minutes before normal production. For ring molds with poor mold hole roughness, sometimes it is necessary to mix 20% to 50% fine sand in the oil for grinding before normal production.

② During the use of the ring die, it is necessary to try to avoid the mixing of large pieces of sand, sand, iron, bolts and iron chips and other hard particles in the material, so as not to speed up the wear of the ring die or cause excessive impact on the ring die, resulting in the ring die Burst. If iron enters the die hole, it must be rushed out or drilled out in time.

③ For the ring die installed symmetrically on both sides, it can be installed and used in reverse after a certain period of production to make the ring die wear evenly.

④ After the ring die is installed, it must not be tilted, otherwise uneven wear will occur; the bolts for fastening the ring die must achieve the required locking torque to avoid bolt shearing and ring die damage.

4. Maintenance of the ring die Reasonable maintenance of the ring die is one of the necessary measures to ensure the normal operation of the ring die and prolong its service life. In normal work, you should pay attention to the following points:

① When the ring mold needs to be replaced, the original feed should be extruded with non-corrosive oil, so that the discharge is smooth when it is used again, and the corrosion of the mold hole can be prevented.

② After the ring die is used for a certain period of time, it should be checked regularly whether there is a local protruding part on the inner surface of the ring die, and whether there is a phenomenon such as grinding, sealing or inversion at the material guide port of the die hole. If so, use a polisher or other tools to smooth the protruding part of the working inner surface of the ring die, and then chamfer the material guide port to carry out necessary repairs to the ring die to prolong the service life of the ring die. When repairing, it should be noted that the lowest part of the working inner surface of the ring die should be 2mm higher than the bottom of the overpass groove, and there is still a margin for adjustment of the eccentric axis of the pressing roller after repair, otherwise the ring die should be scrapped.

③ If most of the die holes are blocked by the material, you can take the method of soaking in oil or cooking in oil to soften the material, and then re-granulation; if it still cannot be granulated, you can use an electric drill to block the die hole. After drilling out, use oily materials and fine sand to grind and use.

④ The ring mold must be stored in a dry and clean place, and the specifications must be marked. If it is stored in a humid place, it may cause corrosion of the ring mold, thereby reducing the service life of the ring mold or affecting the discharge effect. To sum up, only by fully understanding the basic characteristics of the ring mold, and by correctly selecting, using and effectively maintaining the ring mold, can the performance of the granulator and its ring mold be fully exerted, thereby reducing costs, improving granulation efficiency and granulation quality, and creating more economic benefits for the enterprise.